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United States Patent |
5,088,424
|
Sardari
,   et al.
|
February 18, 1992
|
Pollution control apparatus and method for pollution control
Abstract
A method of thermally oxidizing a gaseous component, e.g., including one or
more volatile organic compounds, is disclosed. This method comprises
passing an amount of an oxygen component, a controlled amount of a fuel
component and an amount of a gaseous component to be thermally oxidized to
a combustion zone to combust the oxygen component and the fuel component,
to at least partially thermally oxidize the gaseous component and to form
a gaseous effluent; contacting the gaseous effluent in a retention zone at
conditions effective to thermally oxidize the gaseous component, and
thereby form a flue gas; and controlling the amount of fuel component
passed to the combustion zone based on the temperature in at least one of
said combustion zone and said retention zone contacting occurs. A thermal
oxidation apparatus useful for practicing the present method is also
disclosed.
Inventors:
|
Sardari; Abbas (Laguna Beach, CA);
Von Bargen; John D. (Cypress, CA)
|
Assignee:
|
White Horse Technologies, Inc. (Irvine, CA)
|
Appl. No.:
|
545335 |
Filed:
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June 26, 1990 |
Current U.S. Class: |
110/344; 110/214; 110/234; 110/345 |
Intern'l Class: |
F23J 011/00; F23J 015/00 |
Field of Search: |
110/345,344,234,235,214
|
References Cited
U.S. Patent Documents
3463599 | Aug., 1969 | Welty, Jr. | 110/344.
|
3530807 | Sep., 1970 | Zalman.
| |
3548761 | Dec., 1970 | Zalman.
| |
4078503 | Mar., 1978 | Von Dreushe, Jr. | 110/345.
|
4101632 | Jul., 1978 | Lamberti et al. | 110/345.
|
4206722 | Jun., 1980 | Nolley, Jr. | 110/345.
|
4246853 | Jan., 1981 | Mehta | 110/344.
|
4395958 | Aug., 1983 | Caffyn et al.
| |
4452152 | Jun., 1984 | John et al.
| |
4473013 | Sep., 1984 | John et al.
| |
4485746 | Dec., 1984 | Erlandsson.
| |
4718361 | Jan., 1988 | Berry | 110/345.
|
4726302 | Feb., 1988 | Hein et al. | 110/345.
|
4761132 | Aug., 1988 | Khinkis | 110/345.
|
4846082 | Jul., 1989 | Marangoni | 110/234.
|
4951579 | Aug., 1990 | Bell | 110/214.
|
Primary Examiner: Yuen; Henry C.
Attorney, Agent or Firm: Uxa, Jr.; Frank J.
Claims
What is claimed is:
1. A process for thermally oxidizing a gaseous component comprising:
passing an amount of an oxygen component, a controlled amount of a fuel
component and an amount of a gaseous component to be thermally oxidized to
a combustion zone to combust said oxygen component and said fuel
component, to partially thermally oxidize said gaseous component and to
form a gaseous effluent;
contacting said gaseous effluent in a retention zone located downstream of
said combustion zone at conditions effective to thermally oxidize said
gaseous component, thereby producing a flue gas;
transferring heat from said flue gas, thereby generating a useful product;
controlling the amount of fuel component passed to said combustion zone
based on the temperature in said retention zone, said controlling being
effective to maintain the temperature in said retention zone at at least a
predetermined, minimum value; and
additionally controlling the amount of fuel component passed to said
combustion zone based on the amount of heat to be transferred, provided
that said additional controlling step is effective only when the
temperature in said retention zone is at least about said predetermined,
minimum value.
2. The process of claim 1 wherein said gaseous component includes at least
one volatile organic compound and said flue gas includes the thermally
oxidized product or products of sad volatile organic compound, said
thermally oxidized product or products having increased environmental
acceptability relative to said volatile organic compound.
3. The process of claim 1 wherein said gaseous component to be thermally
oxidized is selected from the group consisting of hydrocarbons,
substituted hydrocarbons and mixtures thereof.
4. The process of claim 1 wherein said oxygen component includes molecular
oxygen, and said fuel component includes one or more hydrocarbon
compounds.
5. The process of claim 1 wherein said combustion zone includes a burner
section in which a combustion flame is initiated, and a combustion chamber
located downstream from said burner section and in which combustion
occurs, and a first portion of said gaseous component is passed directly
to said burner section and a second portion of said gaseous component is
passed directly to said combustion chamber.
6. The process of claim 1 wherein the amount of said gaseous component
passed to said combustion zone is controlled based on the pressure of the
gaseous component upstream of the point at which the amount of said
gaseous component passed to said combustion zone is controlled.
7. The process of claim 1 wherein said transferring heat from said flue gas
generates steam and which further comprises controlling the amount of said
steam generated.
8. The process of claim 7 wherein said steam generation controlling step
includes controlling the flow path of said flue gas.
9. The process of claim 7 wherein the amount of said steam generated is
controlled based on the pressure of the generated stream.
10. The process of claim 1 wherein said transferring heat from said flue
gas generates steam and said additional controlling step includes
monitoring the pressure of the steam generated.
11. The process of claim 1 wherein said transferring heat from said flue
gas generates steam and said additional controlling step includes
controlling the amount of oxygen component passed to said combustion zone
based on the amount of steam to be generated.
12. The process of claim 11 wherein said additional controlling step
includes monitoring the pressure of the steam generated.
13. A process for thermally oxidizing a gaseous component comprising:
passing an amount of an oxygen component, a controlled amount of a fuel
component, and an amount of gaseous component to be thermally oxidized and
including at least one volatile organic compound to a combustion zone to
combust said oxygen component and aid fuel component, to at least
partially thermally oxidize said gaseous component and to form a gaseous
effluent;
contacting said gaseous effluent in a retention zone located downstream
from said combustion zone at conditions effective to thermally oxidize
said gaseous component, thereby producing a flue gas including the
thermally oxidized product or products of said volatile organic compound,
said thermally oxidized product or products having increased environmental
acceptability relative to said volatile organic compound;
transferring heat from said fuel gas to generate steam;
controlling the amount of said fuel component passed to said combustion
zone based on the temperature in said retention zone, said controlling
being effective to maintain the temperature in said retention zone at at
least about a predetermined, minimum value; and
additionally controlling the amount of aid fuel component passed to said
combustion zone based on the amount of steam to be generated, provided
that said additional controlling step is effective only when said
temperature in said retention zone is at least about said predetermined,
minimum value.
14. The process of claim 13 wherein said additional controlling step
includes controlling the amount of oxygen component passed to said
combustion zone based on the amount of steam to be generated.
15. The process of claim 15 wherein said oxygen component includes
molecular oxygen, said fuel component includes one or more hydrocarbon
compounds, and said gaseous component to be thermally oxidized is selected
from the group consisting of hydrocarbons, substituted hydrocarbons and
mixtures thereof.
Description
BACKGROUND OF THE INVENTION
This invention relates to a method and apparatus for thermally oxidizing a
gaseous material, e.g., a gas and/or vapor, in particular a gaseous
material including volatile organic compounds or components. In
particular, this invention relates to a method and apparatus for thermally
oxidizing such gaseous material to render the gaseous material more
environmentally acceptable and, preferably, to usefully transfer the heat
evolved in such thermal oxidation, e.g. to thereby generate steam and/or
hot water and/or hot oil.
Environmental concerns are becoming increasingly important, particularly in
industries which produce, e.g., as primary products and/or by-products,
volatile organic compounds or components, hereinafter referred to as VOC,
which are released to the environment. Regulatory authorities have
required that such VOC, in particular VOC which are hazardous to the
health and/or safety of humans and/or other organisms, be treated to
become and/or provide products which are more environmentally acceptable
than the original VOC.
One useful approach to this pollution problem involves thermally oxidizing
the VOC to produce materials which can be readily and safely released to
the atmosphere. During the thermal oxidation of such VOC, a substantial
amount of heat is produced. In certain instances where VOC is thermally
oxidized, the resulting flue gases have been passed through a waste heat
boiler installation to produce or generate steam and/or hot water. One
problem which has arisen in the past is the process control of such a VOC
thermal oxidation/waste heat boiler installation facility. This problem is
particularly acute since the production of VOC to be thermally oxidized
and the amount of steam/hot water required from the facility can be
independent of each other.
Previous control systems have controlled the amount of added fuel, e.g.,
natural gas, propane, diesel fuel and the like, fed to the thermal
oxidizer and the amount of air fed to the thermal oxidizer solely to
regulate VOC emissions from the process. When steam demand is low, the
fuel and air fed to the thermal oxidizer is maintained at a relatively
high level so as to insure VOC thermal oxidation. Such control systems
result in a substantial amount of energy being wasted by exhausting hot
flue gases to the atmosphere. Moreover, previous systems utilized to
destroy gaseous materials utilized very severe conditions which often
involved unneeded combustion, which combustion itself often resulted in
unnecessary air pollution.
In certain solid waste incinerators, the temperature in the combustion
chamber is used to control the amount of fuel fed to the incinerator. See
Zalman U.S. Pat. Nos. 3,530,807 and 548,761. However, in neither of these
systems is gaseous material fed to a thermal oxidizer for thermal
oxidation. Separate steam generators are employed in these systems. In
addition, no steam is produced outside the combustion chamber itself, or
for use elsewhere than in the incinerator to scrub particulates from the
exhaust gas.
It would be clearly advantageous to provide a system which is controlled to
provide effective and efficient thermal oxidation and useful heat transfer
with controlled, e.g., reduced, fuel consumption.
SUMMARY OF THE INVENTION
A new thermal oxidation method and apparatus has been discovered. The
present thermal oxidizing system is particularly useful in treating
gaseous components, especially gaseous components containing one or more
volatile organic compounds or components (VOC). As used herein, the term
"gaseous component" refers to gases and mixtures thereof, and to gases and
mixtures thereof which include entrained liquids, i.e., vapors. In
addition, the present system preferably provides cost effective and
controlled amounts of useful heat transfer, in particular for the
generation of steam and/or hot water and/or hot water and/or the like,
especially steam. The present system utilizes temperature control to
ensure that the compound or compounds in the gaseous component to be
thermally oxidized or treated are effectively thermally oxidized or
treated, e.g., destroyed, modified or converted into a compound or
compounds which are more environmentally acceptable than the original
compound or compounds in the gaseous component fed to the system. This is
accomplished in such a manner so that controlled, and preferably reduced,
amounts of added fuel, e.g., natural gas, propane, diesel fuel, other
petroleum distillates, petroleum residua and the like, are used. Further,
the amount of useful heat transfer preferably achieved in such a thermal
oxidation system is controlled to meet the demand for such heat transfer,
e.g., the demand for steam and/or hot water. In short, the present system
provides for effective pollution control by thermal oxidation while
controlling the amount of fuel utilized for such pollution control thermal
oxidation.
In one broad aspect, the present invention is directed to a method for
thermally oxidizing a gaseous component, in particular VOC. This method
comprises passing an amount of an oxygen component, a controlled amount of
a fuel component and the gaseous component to be thermally oxidized to a
combustion zone to combust the oxygen component and the fuel component, to
at least partially thermally oxidize the gaseous component, preferably to
a product or products which are more environmentally acceptable than the
original gaseous component, and to form a gaseous effluent. This gaseous
effluent is contacted in a retention zone, which may be a portion of the
combustion zone, e.g., a portion of the combustion chamber, and/or may be
located away from, e.g., downstream of, the combustion zone, at conditions
effective to thermal oxidize the gaseous component and to form a flue gas,
which may be exhausted to the atmosphere.
The present method involves controlling the amount of fuel component passed
to the combustion zone based on the temperature in at least one of the
combustion zone and the retention zone. The present retention zone is
maintained at conditions, in particular a temperature, at which thermal
oxidation of the gaseous component can occur. The temperature control
mechanism described above effectively controls the amount of fuel
component added to the combustion zone so as to reduce the cost of such
thermal oxidation. This approach is substantially different from prior art
systems for thermally oxidizing gaseous materials in which fuel and oxygen
were provided without regard to the temperature in the combustion chamber
or downstream of the combustion chamber.
In a particularly useful embodiment, the present method further comprises
providing means to transfer heat from the flue gases to generate a useful
product, e.g., steam, hot water, hot oil and the like, in particular
steam. The amount of useful product, e.g., steam, generated is preferably
controlled. For example, the amount of useful product generated can be
controlled by controlling the flow path of the flue gases. Thus, depending
upon the amount of useful product to be produced, the flue gases can be
exhausted directly to the atmosphere or can be passed through a heat
exchange system, e.g., a boiler, to produce the desired amount of useful
product.
In one useful embodiment, the temperature controlling step is effective to
maintain the temperature in at least one of the combustion zone and the
retention zone, preferably the retention zone, at at least about a
predetermined, minimum value. This method preferably further comprises
additionally controlling the amount of fuel component, and more preferably
the amount of oxygen component, passed to the combustion zone based on the
amount of useful product to be generated. This additional controlling step
is effective only when the temperature in at least one of the combustion
zone and the retention zone, preferably the retention zone, is at at least
about the predetermined minimum value. This predetermined minimum value is
selected to ensure that the gaseous component to be thermally oxidized is
substantially completely thermally oxidized prior to leaving the retention
zone. This additional controlling step preferably includes monitoring the
pressure of the steam generated and, more preferably adjusting the amount
of fuel component, and still more preferably oxygen component, fed to the
combustion zone based on this pressure.
In another broad aspect of the present invention, an apparatus for thermal
oxidizing a gaseous component, preferably VOC, comprises a combustion
zone, a retention zone and control means. The combustion zone is sized and
adapted to receive an amount of an oxygen component, a controlled amount
of a fuel component, and an amount of gaseous component to be thermally
oxidized and to provide a location for the combustion of the oxygen
component, preferably including molecular oxygen, and the fuel component,
preferably a hydrocarbon-based fuel such as those described elsewhere
herein and the like, and at least the partial thermal oxidation of the
gaseous component and the formation of a gaseous effluent. The retention
zone, which may be a portion of the combustion zone and/or may be located
away from the combustion zone, preferably located downstream of the
combustion zone, provides a location where the gaseous effluent is passed
and where the gaseous effluent is maintained at conditions effective to
thermally oxidize the gaseous component, and where a flue gas is formed.
The control means acts to control the amount of fuel component passed to
the combustion zone based on the temperature in at least one of the
combustion zone and the retention zone, preferably in the retention zone.
Preferably, the present apparatus further comprises means acting to
transfer heat from the flue gas and generate a useful product, e.g., as
described elsewhere herein, in particular steam. More preferably, the
present apparatus further comprises product control means acting to
control the amount of useful product, e.g., steam, generated.
The combustion zone preferably includes a burner section in which a
combustion flame is initiated (e.g., through the use of a pilot light) and
maintained, and a combustion chamber, preferably located downstream from
the burner section, in which combustion occurs. In one embodiment, a
portion of the gaseous component is preferably passed directly to the
burner section, while another portion of the gaseous component is passed
directly to the combustion chamber. The present apparatus preferably
further comprises additional control means acting to control the amounts
of fuel component, and more preferably oxygen component, passed to the
combustion zone based on the amount of useful product, e.g., steam to be
generated. This additional control means is activated only when the
temperature in at least one of the combustion zone and the retention zone,
preferably the retention zone, is at at least about a predetermined,
minimum value.
In another embodiment, the present apparatus further comprises gaseous
component control means acting to control the amount of the gaseous
component passed to the combustion zone, preferably based on the pressure
of the gaseous component upstream of the control point.
These and other aspects and advantages of the present invention are set
forth in the following detailed description and claims, particularly when
considered in conjunction with the accompanying drawing in which like
parts bear like reference numerals.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a generally schematic view of one embodiment of a thermal
oxidation/steam generation apparatus in accordance with the present
invention.
DETAILED DESCRIPTION OF THE DRAWING
Referring now to FIG. 1, a thermal oxidation/steam generation apparatus in
accordance with the present invention, shown generally at 10, includes a
gas intake assembly 12, a fuel intake assembly 14, a combustion zone 16
and a boiler section 20. The apparatus 10 is controlled, as discussed in
detail hereinafter, from a centralized control panel 22. The various
components of control panel 22 may be selected from conventional and
commercially available components which individually or together are
useful to receive and transmit the control signals and alarm signals
described herein. Examples of commercially available devices suitable for
use as control panel 22 include burner management systems sold by Fireye,
Inc. and Honeywell, Inc. Although each of the parts of apparatus 10 is
discussed separately, the proper functioning of apparatus 10 depends on
each of these parts working together effectively.
Gas intake assembly 12 includes a gas feed line 24 which passes
VOC-contaminated air into apparatus 10, e.g., from one or more
manufacturing facilities and/or storage facilities. Substantially any VOC
or mixture thereof can be thermally oxidized in accordance with the
present invention. For example hydrocarbons, substituted hydrocarbons,
other organic compounds, mixtures thereof and the like can be thermally
oxidized. Such VOC may be hazardous and/or non-hazardous. The amount of
VOC-contaminated air which is passed to apparatus 10 varies from time to
time. A VOC intake damper 26 is operated by damper motor 28 which, in
turn, is controlled based on the pressure sensed by pressure sensor 30.
The damper motors employed in apparatus 10 may be chosen from conventional
and well known motors of this type, and may be powered electrically or
pneumatically. The pressure sensors described herein may be of
conventional design. The pressure sensed by pressure sensor 30 is at a
point upstream of VOC intake damper 26 in feed line 24. The use of VOC
intake damper 26 aids in controlling the suction pressure to air blower
32.
A fresh air inlet line 46 is provided to pass fresh air into apparatus 10
when needed. A fresh air damper 48, located in line 46 is positioned to
allow fresh air to pass into air blower 32 or to be closed to such
passage. Fresh air damper 48 is operated by damper motor 50 which is
controlled by signals received from control panel 22 through control
signal line 51. Fresh air damper 48 is closed when the amount of
VOC-contaminated air from line 24 is sufficient to provide for the desired
operation of apparatus 10. If additional air is required for such
operation, e.g., to generate the desired amount of steam, fresh air damper
48 is opened to provide the same. In different alarm situations, fresh air
damper 48 may be opened or closed depending on the specific alarm
situation involved.
Both VOC-containing air gas feed line 24 and fresh air line 46 feed into
blower inlet line 42. A blower inlet damper 44 is provided in line 42 and
is normally positioned to allow passage of VOC-containing air into blower
32. However, in certain alarm situations, blower inlet damper 44 is moved
to a closed positioned by operator 38 (which may be powered electrically
or pneumatically) in response to signals received from control panel 22
via signal line 40. An emergency by-pass line 34 is provided with a
by-pass damper 36, which is normally closed. In certain alarm situations,
damper 36 is opened by operator 38 in response to signals received from
control panel 22 via control signal line 40. Ordinarily, if by-pass damper
36 is closed, inlet damper 44 is open, and vice versa.
The air blower 32 pressurizes the gas in blower inlet line 42 in advance of
such gas entering the combustion zone 16. Air blower 32 may be one of a
number of conventional and well known devices such as, for example,
blowers sold by Garden City Fan Company and New York Blower Company.
The VOC-containing air passes from air blower 32 through line 54 into a
flash-back prevention system 56 which includes a section 58 of conduit
which has a reduced cross-sectional area for fluid flow relative to line
54. A differential pressure sensor 60 monitors the difference in fluid
pressure in line 54 and in section 58. If this difference falls below a
predetermined minimum, an alarm signal is passed from pressure sensor 60
through signal line 61 to control panel 22 which, in turn, closes damper
42 and opens damper 36 to vent the VOC-containing air from line 24 to the
atmosphere, and opens damper 48 to allow fresh air from line 46 to pass to
air blower 32. Flash-back prevention system 58 is, in effect, a velocity
monitor, and also protects the air blower 32 from being exposed to hot
gases which are located downstream of air blower 32.
After the flash-back prevention system 56, VOC-containing air is passed
through line 62 into combustion zone 16, which includes a burner section
64 and a chamber 66, which acts primarily as a combustion chamber. A
portion of chamber 66, in particular the downstream portion 67 of chamber
66 further acts as a preliminary retention chamber. A fuel material, e.g.,
a hydrocarbon fuel such as natural gas, propane, diesel fuel and the like,
is also passed to the combustion zone 16 using fuel intake assembly 14.
The fuel intake assembly 14 includes a fuel source 68, a series of valves,
and a control valve 70, which is operated by valve motor 72. The various
valves and valve motor 72 of fuel intake assembly 14 can be of
conventional design. The amount of fuel fed to the combustion zone 16
through fuel supply line 74 is controlled by using valve motor 72 to vary
the position of control valve 70. Valve motor 72 is operated in response
to a signal from control panel 22 passed through signal line 76. In
addition, safety valve 78 upstream of control valve 70 in line 74 is
operated by a safety switch 80 which acts to shut or close safety valve 78
when it is activated to do so by an alarm signal from control panel 22
passed to safety switch 80 through signal line 82.
Both the VOC-containing air from line 62 and the fuel from line 74 are fed
into the burner section 64 where a flame 84 is ignited and maintained. The
combustion zone 16, e.g., burner section 64 and chamber 66, may be of
conventional design. In certain designs, the VOC-containing air from line
62 can be split into two separate streams, with one portion being fed to
the burner section 64 and the other portion being fed directly to the
chamber 66. This embodiment is illustrated by line 86 (shown in shadow)
passing from line 62 directly into chamber 66 and by-passing burner
section 64. The use of this "split-air stream" embodiment is particularly
useful if a low NOX (nitrogen oxide) premix burner is employed in the
burner section 64.
The conditions in the burner section 64 and chamber 66 are sufficient to
combust the fuel and oxygen fed to combustion zone 16. Excess oxygen is
preferably present to provide for substantially complete combustion of the
fuel. In addition, at least a portion of the VOC in the VOC-containing air
fed to the combustion zone 16 is effectively thermally oxidized in the
combustion zone 16 to form one or more compounds which are more
environmentally acceptable than the compound or compounds making up the
VOC fed to apparatus 10.
The hot effluent gases from the chamber 66 pass to an additional chamber 88
located downstream of chamber 66. Additional chamber 88 may be considered
an extension of chamber 66. Here, in additional chamber 88, with the
temperature maintained at or above a predetermined minimum value, e.g., at
least about 1400.degree. F., and oxygen available, the remaining VOC, if
any, from the original VOC-containing air is effectively thermally
oxidized. As shown in FIG. 1, the size of the additional chamber 88 can be
varied to suit the particular application involved and to provide
sufficient residence time for effective VOC thermal oxidation. Thus, in
FIG. 1, an additional, variable length 90 (shown in shadow) of additional
chamber 88 can be provided, if desired. The size and/or configuration of
additional chamber 88 may influence the size and/or configuration of
chamber 66. Additional chamber 88, and possibly downstream portion 67, is
conveniently lined with high temperature insulation, refractory, ceramic
or the like to retain heat. Existing installations, e.g., boilers, may be
retrofitted in accordance with the present invention by, for example,
replacing the existing combustion system with a new combustion system,
such as combustion zone 16 and/or modifying the installation to provide an
effective retention zone, such as by lining an area downstream of the
burner with high temperature insulation, refractory, ceramic or the like.
An important feature of apparatus 10 is a temperature sensor 92, e.g., a
conventional thermocouple, which measures or senses the temperature in
additional chamber 88 downstream from chamber 66 and passes a temperature
signal to control panel 22 through signal line 94. Alternately a
temperature sensor 93 (shown in shadow) can be used to measure or sense
the temperature in chamber 66 and pass a temperature signal to control
panel 22 through signal line 95. If the temperature in additional chamber
88 (or in chamber 66, in particular in downstream portion 67) is below a
predetermined, minimum value, e.g., about 1200.degree. F. to about
1500.degree. F., in particular about 1400.degree. F., control panel 22
sends a signal to fuel intake assembly 14 through signal line 76 to
increase the amount of fuel passed to combustion zone 16. In this manner,
the temperature in additional chamber 88 (or downstream portion 67) is
controlled to provide effective conditions for VOC thermal oxidation. The
additional chamber 88 is chosen to be compatible, e.g., in size and
materials of construction, with the other components of the system and to
effectively thermally oxidize any VOC passing from the combustion zone 16.
The flue gases produced in additional chamber 88 pass into boiler section
20 where steam is produced based on steam demand in a plant steam line 96.
In effect, the flue gases from additional chamber 88 have two alternative
paths through boiler section 20. First, if steam demand is low, the flue
gases can pass through conduit 98, past exhaust damper 100, which is open,
and into exhaust conduit 102 through which it is passed and allowed to
escape to the atmosphere. Alternately, if steam demand is high, exhaust
damper 100 is closed and the flue gases from conduit 98 are forced to pass
through heat exchange tubes 104 where heat is removed from the flue gases
and used to heat water in a shell, illustrated schematically at 106, and
generate steam which leaves by plant steam line 96. In certain
applications, the exhaust conduit 102 and exhaust damper 100 are not
present so that the flue gas is forced to pass through heat exchange tubes
104. After this heat exchange operation, the cooled flue gases pass
through cool exhaust conduit 108 and are exhausted to the atmosphere. The
heat exchange system of boiler section 20 may be of conventional design.
The operation of boiler section 18 is controlled as follows. Two pressure
sensors 110 and 112 monitor the pressure in shell 106. Pressure sensor 110
is associated with an exhaust damper motor 114 and controls its operation.
If the pressure sensed by pressure sensor 110 is above a predetermined
maximum value, a signal is passed through signal line 113 to exhaust
damper motor 114 which is activated to open exhaust damper 100. This
reduces the amount of steam generated and allows the flue gas to exhaust
through exhaust conduit 102. If the pressure sensed by pressure sensor 110
is below a predetermined minimum value, exhaust damper motor 114 is
activated to close exhaust damper 100 and cause the flue gases to pass
through tubes 104 and generate increased amounts of steam. Pressure sensor
110 also provides signals, through signal line 116, to control panel 22 to
warn of (or provide an alarm for) high pressure in shell 106.
Pressure sensor 112 is associated with control panel 22 by signal line 118.
When pressure sensor 112 senses a pressure in shell 106 below a
predetermined minimum value (an indication that steam demand is high), a
signal is passed through signal line 118 to control panel 22 which, in
turn, sends signals to the fuel intake assembly 14 to increase the amount
of fuel sent to combustion zone 16. In addition, if the amount of
VOC-containing air in line 42 is insufficient to combust the increased
amount of fuel, control panel 22 also sends a signal to gas intake
assembly 12 to increase the amount of fresh air passed to combustion zone
16.
Alternately, an exhaust conduit damper 109 (shown in shadow) in exhaust
conduit 108 may be used to control the path of the flue gas. Thus, damper
109 is driven by exhaust conduit damper motor 111 (shown in shadow) which
operates in response to the pressure sensed by pressure sensor 110. When
steam demand decreases, pressure sensor 110 provides a signal through
signal line 116 to control panel 22 which, in turn, sends a signal through
signal line 119 to damper motor 111 to close damper 109. This causes the
pressure in conduit 98 to increase. This increased pressure is sensed by
pressure sensor 115 (shown in shadow) which passes a signal through signal
line 117 to exhaust damper motor 114 to open exhaust damper 100, thus
exhausting the flue gas to the atmosphere. By reverse analogy, when steam
demand increases, this alternate system functions to open exhaust conduit
damper 109 and close exhaust damper 100.
Although the embodiment illustrated shows heat transfer to generate steam,
and steam generation is preferred, the present invention is applicable to
employing heat transfer from the flue gas to generate other useful
products, such as hot water, hot oil and the like, instead of, or in
combination with, steam generation. The generation employing flue gas heat
transfer of such other useful products is within the scope of the present
invention.
As can be seen from the above description, the VOC fed to apparatus 10 is
effectively thermally oxidized, while controlling the amount of fuel used.
In addition, increased amounts of steam can be produced when steam demand
is high. The present system employs strategically placed sensors,
preferably both temperature and pressure sensors, to control the present
thermal oxidation/steam generation system to achieve the desired results
while controlling the amount of fuel employed.
While this invention has been described with respect to various specific
examples and embodiments, it is to be understood that the invention is not
limited thereto and that it can be variously practiced within the scope of
the following claims.
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